Nomad is fought a total of four times during the quest.
In the first fight when Nomad says "Feel the power of Gielinor", move from your current spot or Gielinor will slam the ground with one of his hands and cause up to 4k damage. Gielinor has a special attack that fires purple magic attack causing up to 800 lifepoints of damage, this can be avoided by moving.
In this second Nomad fight there is a new attack at avoid. When Nomad says "Can you handle my wrath!" hide behind a pillar to block the damage or you will loose 7.5k lifepoints.
In this fight, Nomad will attack with the three previous attacks and at half health Nomad will split into two, you will have to defeat the original Nomad, if you are lucky and defeat the original the other version of him will disappear, if not you will need to defeat the remain half.
This time it is a straight forward fight with no special attacks. After defeating Nomad, a cut-scene will start and you can choose Death or Icthlarin to kill Gielinor.